conf: Ignore multiqueue with one queue.

Multi != One.  And indeed, libvirt behaves the same way for queues='1'
as without such setting.  Let's make it clear in the XML.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/conf/domain_conf.c

@@ -8626,7 +8626,8 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
                                queues);
                 goto error;
             }
-            def->driver.virtio.queues = q;
+            if (q > 1)
+                def->driver.virtio.queues = q;
         }
         if ((str = virXPathString("string(./driver/host/@csum)", ctxt))) {
             if ((val = virTristateSwitchTypeFromString(str)) <= 0) {

tests/qemuxml2argvdata/qemuxml2argv-tap-vhost-incorrect.xml

@@ -28,6 +28,12 @@
       <driver name='vhost' queues='5'/>
       <backend tap='/dev/null' vhost='/dev/zero'/>
     </interface>
+    <interface type='user'>
+      <mac address='52:54:00:e5:48:59'/>
+      <model type='virtio'/>
+      <driver name='vhost' queues='1'/>
+      <backend tap='/dev/null' vhost='/dev/zero'/>
+    </interface>
     <serial type='pty'>
       <target port='0'/>
     </serial>

tests/qemuxml2xmloutdata/qemuxml2xmlout-tap-vhost-incorrect.xml

@@ -27,6 +27,12 @@
       <model type='definitely-not-virtio'/>
       <backend tap='/dev/null'/>
     </interface>
+    <interface type='user'>
+      <mac address='52:54:00:e5:48:59'/>
+      <model type='virtio'/>
+      <driver name='vhost'/>
+      <backend tap='/dev/null' vhost='/dev/zero'/>
+    </interface>
     <serial type='pty'>
       <target port='0'/>
     </serial>